Roller target for checking concentricity of machined bore



June 14, 1966 c. R. JOHNSON 3,255,530

ROLLER TARGET FOR CHECKING CONCENTRICITY 0F MACHINED BORE Filed March 22, 1965 //V VE N T 0/? CLAUDE R. JOHNSON Attorney United States Patent 3 255 530' ROLLER TARGET FoR CHECKING CONCEN- TRICITY or MACHINED BORE I Claude R. Johnson, Pittsburgh, Pa., assignor to United States Steel Corporation, a corporation of New Jersey Filed Mar. 22, 1963, Ser. No. 267,144 6 Claims. (Cl. 33-46) ship shafts, the central core is often removed by a series of machining operations. Providing the forging with a hollow core enhances subsequent heat treatment. Furthermore, it eliminates any uncertanity about traces of piping or segregation that may have escaped detection by discard or close inspection. Also, a considerable reduction in weight'may be made with no appreciable loss in the eflective strength of the forging.

The machining operations must be very accurate so that the resulting bore is located concentric to the longitudinal axis of the forging. After machining, the lathe tailstock is backed away from the workpiece and it is supported by one or more steady rests along its length while still being secured by the chuck jaws of the lathe headstock. In the past, the concentricity of the bore was measured by the use of a long bar to which was secured a roller positioned atright angles to its length, but such means has several serious disadvantages.

This whole operation, as conducted with such means, was very .slow, tedious and could not be depended upon for restricted accuracy. It is therefore an object of my invention to provide improved apparatus for accurately and expeditiously determining the concentricity of the bores of workpieces.

A more specific object is to provide a roller target for sighting thereon at spaced positions in a machined bore to determine bore concentricity, said target comprising a longitudinal shaft, a wheel journaled thereon adjacent each end, a target mounted normal to the shaft, and a counterweight on the shaft adapted to maintain the target constantly in a substantially vertical position.

A further object to provide an apparatus utilizable for determining concentricity of a machined bore in an elongated workpiece by placing in the bore a counterweighed target rolling on the interior thereof, adapted to maintain a substantially vertical position, intermittently rotating the workpiece about a horizontal axis, then sighting on a line parallel to the axis and normal to the target, moving the target progressively along the bore until the bore is traversed and repeating the sighting after each movement of the target.

In accomplishing these and other objects of the invention, I have provided a preferred form of apparatus shown in the accompanying drawings. In the drawings:

FIGURE 1 is a perspective view, partly cut away, showing the roller target of invention and the manner of its use in determining bore concentricity;

FIGURE 2 is an enlarged perspective view of the roller target;

FIGURE 3 is a vertical section of the target; and

FIGURE 4 is a view taken on line IVIV of FIGURE 3 showing a switch detail.

As shown in FIGURES 2 and 3, the roller target comprises a shaft 10 having bearings 12, 14 pressed thereon adjacent the ends and mounting wheels 16, 18, respectively. The rolling edges 20, 22 of the wheels may be rimmed with a hard-wearing material. A third bearing ice 24 is pressed on one end of shaft 10, adjacent bearing 12, and a disc 26 is mounted thereon. Between the wheels, shaft 10 has a recess 28 opening upwardly. The lower portion 30 of the shaft left intact serves as a counterweight.

Recess 28 carries a dry cell 32. A protective cover 34 therefor, which also-holds cell 32 in place, is bolted to the shaft. Shaft 10 is bored axially, providing a foremost hole 36 and a rearmost hole 38. The forward end of hole 36 is threaded to receive a socket 40, which in turn receives a lamp 42. An insulating sleeve 44, made of fiber or the like, fits in the hole 36 behind socket 40. The sleeve has a copper pin 46 therein, serving as a conductor between lamp 42 and dry cell 32. Hole 38 carries a copper pin 48, which may also 'be encased in an insulating sleeve. Pin 48 has disc-like enlargements 50, 52 on the opposite ends thereof. Enlargement has a spring 54 mounted therebehind on pin 48, urging the pin into contact with dry cell 32. Knurled knob 52 has an offset portion 56 thereon. As shown in FIGURE 4, olfset portion' 56 may be oblong in cross section and is adapted to mate with a slightly larger oblong depression 58 in the end of shaft 10, whereby pin 48 is permitted to make contact with' dry cell 32 and complete the circuit. Lamp 42 is then lighted. Thus, pin 48 serves as a switch in a light circuit, lamp 42 being turned on and off by turning the knurled knob about 90 from its previous position.

Extending forwardly from shaft 10 or more particularly from disc 26, is a housing 60 having a U-shaped flange 62 thereon bolted to disc 26. Housing 60, preferably of aluminum or other light-weight material, is machined to provide a recess 64 therein, opening upwardly and rearwardly. A target 66 is mounted normal to the axis of shaft 10 in the rearward portion of recess 64. The target slides in spaced vertical grooves 65a and 65b in the edges of flange 62. The target is held firmly against the outer face of disc 26, when flange 62 is bolted thereagainst. A scale 68 is inscribed on target 66 as a series of horizontal lines, preferably spaced 0.1" apart, from either side of a center or Zero line. Extending from its socket 40 through an opening 70 in disc 26, bulb 42 is positioned below target 66. The forward end 72 of housing 66 supports a mirror 74 at an angle to reflect the light from lamp 42 on the target.

A stub shaft 76 is journaled in a bearing 78, mounted in end block'72. A plate 80, bolted to end block 72, holds bearing 78 in position. A measuring tape 82 is attached to stub shaft 76 by means of an articulated flexible connection 84. A counterweight 86 is mounted on the underside of disc 26 by a set screw 88.

In use, my roller target, when in a rotating machined bore, rolls on wheels 16, 18 and when allowed to come to rest, assumes the position shown in FIGURES 2 and 3. Between the wheels, recess 28 always opens upwardly because the lower portion 30 serves as a counterweight. Disc 26 is rotated on bearing 24 by counterweight 86 to substantially the same position at all times. This in turn maintains housing 60 and target 66 in a vertical position and the lines on scale 68 in a horizontal position. The stub shaft 76 is mounted in a bearing and is in turn connected to a chain or measuring tape 82 by means of an articulated flexible connection to avoid any binding or twisting in these connections. This arrangement is preferred, since it is conceivable that the measuring tape 82 may become twisted and that its weight may force housing 60 and more particularly target 66 from its vertical position.

It is, of course, possible to illuminate target 66 from outside the bore and to provide a simpler structure for the roller target. Such a structure may comprise a shaft having a wheel journaled on the shaft adjacent each end thereof. A target may be mounted normal to and on one end of the shaft. The target would be held in substantially vertical position by a counterweight attached to the underside of the shaft. A measuring tape may also be attached to this end of the shaft.

The method of using my roller target to determine the concentricity of a machined bore 90 in a workpiece 92 is shown in FIGURE 1. One or more steady rests 94, supported on a base 96 and fitted with rollers 98, support workpiece 92 for rotation by a lathe or other means, not shown. After lighting lamp 42, the roller target is inserted in bore 90 and is pushed to the end engaged by the lathe head-stock by means of a long rod. The end face of workpiece 92 may be divided into quadrants or other divisions by chalk markings. At an appropriate distance from workpiece 92 there is mounted a transit 100, including a telescope 102 and an optical micrometer 104. The optical micrometer has a range of 0.1 each way from zero. It is operated by a drum calibrated to .001". The complete transit is a stock instrument which may be purchased on the open market. Its use and adjustment for the stated purpose are known in the art.

Initially, transit 100 is adjusted so that telescope 102 sights on a line parallel to the axis of bore 90 and normal to target 66. With the optical micrometer 104 set at zero, the transit is adjusted until the crosshairs in the micrometer intersect the zero line on scale 68. Thereafter, workpiece 92 is rotated intermittently, for example, through about 90". After each complete revolution, the target is pulled forward by means of tape 82, for example, about two feet. The intermittent rotation is repeated. The transit is sighted on the roller target after each 90 of workpiece rotation. Thereafter, the drum on optical micrometer 104 is turned in either direction to bring the crosshairs back to the zero line on the scale. The optical micrometer is then read to determine the variation in thousandths of an inch from the previous reading. F or the described optical micrometer, this variation in either direction from the zero position of its drum may be up to 0.1", the capacity of the drum.

Since the lines on scale 68 are 0.1" apart, should the variation between sightings be greater than that distance, the crosshairs are brought back to one of these lines and the reading added to one or more line spacings, as the case may be. When all the readings taken after each sighting are recorded, the differences in the high and low readings would indicate therun-out or concentricity of the machined bore, along the length of the workpiece. Usually, the finish machining of the outside of the workpiece will then be effected to compensate for the bore concentricity and to provide a uniform wall thickness throughout the workpiece.

The invention is characterized by several distinct advantages. In the first place, the roller target, since it is counterweighted and always assumes a perpendicular position, will quickly cease its oscillation after the workpiece has been turned, thereby permitting sighting thereon without undue delay. Secondly, the entire bore of a workpiece may be explored relatively quickly with respect to its concentricity by first positioning the roller target at the far end of the bore, then pulling it predetermined distances toward the transit with its measuring tape. Lastly, the roller target, as described above, may be simple or more elaborate in construction depending somewhat on the roughness or fineness of the machining operation and on the over-all convenience that is preferred.

Although I have disclosed herein the preferred practice and apparatus of invention, I intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention.

I claim:

1. A roller target adapted to be disposed at spaced positions along a machined bore for determination of bore concentricity, comprising a shaft, a Wheel journaled on said shaft adjacent each end thereof, a target mounted normal to said shaft, and a counterweight on said shaft adapted to maintain said target substantially vertical.

2. Apparatus as defined in claim 1 characterized by said shaft having a recess between said wheels opening upwardly, leaving the lower portion of the shaft to serve as a counterweight, said recess being adapted to receive a dry cell, a lamp mounted adjacent said target, and a circuit including a switch connecting said dry cell and lamp.

3. Apparatus as defined in claim 2 characterized by a mirror mounted adjacent said target and adapted to reflect light from said lamp onto said target.

4. Apparatus as defined in claim 2 characterized by an axial hole through said shaft, a socket for said lamp formed in one end of the foremost hole, an insulating sleeve therebehind in said hole and a conductor therein connecting said lamp and dry cell, a switch comprising a conductor in the rearmost hole, an enlargement on each end thereof, said rearmost enlargement being provided with an offset portion thereon adapted to mate with a depression in said shaft each time the switch is turned and a spring urging the foremost enlargement into contact with said dry cell thereby completing the circuit.

5. Apparatus as defined in claim 1 characterized by a bearing onsaid shaft adjacent each end thereof mounting one of the wheels, a third bearing journaled on said shaft outwardly of the adjacent first-mentioned bearing, and a disc mounted thereon, said target being mounted on said disc normal to said shaft, and a counterweight attached to the underside of said disc adapted to keep said target substantially vertical.

6. Apparatus as defined in claim 1 characterized by a housing extending outwardly from one end of said shaft, a source of light positioned in said housing, and a mirror positioned in said housing at a light-reflecting angle to said target.

References Cited by the Examiner UNITED STATES PATENTS 1,035,426 8/1912 Dixon. 2,198,837 4/1940 Morgan 3346 2,466,698 4/1949 Getler 3346 2,538,475 1/1951 Skrastin 33--74 X 2,684,434 7/1954 Burey 3374 X ROBERT B. HULL, Primary Examiner. 

1. A ROLLER TARGET ADAPTED TO BE DISPOSED AT SPACED POSITIONS ALONG A MACHINED BORE FOR DETERMINATION OF BORE CONCENTRICALLY, COMPRISING A SHAFT, A WHEEL JOURNALED ON SAID SHAFT ADJACENT EACH END THEREFO, A TARGET MOUNTED 